Horizontal levees are a recently developed nature-based approach to protecting existing communities from sea level rise and creating wetland habitat while simultaneously improving water quality. A horizontal levee consists of a gradually-sloped subsurface wetland with fine surface substrates that facilitate native plant growth and a woodchip-amended coarse sediment layer starting at about 0.3 meters below the ground surface. To test the ability of horizontal levees to improve water quality, we designed, built and studied a 7000 m<sup>2</sup> experimental horizontal levee that received nitrified secondary treated wastewater effluent. During the first 3 years of operation, we observed near complete removal of nitrate and trace organic contaminants (e.g. pharmaceuticals) within the first 10 meters of the wetland when flows were limited to the subsurface. A section of the wetland also was used to treat reverse osmosis concentrate from a municipal wastewater reuse project. Spatially-resolved porewater sampling in sections of the levee receiving either effluent or reverse osmosis concentrate indicated rapid removal of nitrate, some trace metals and most trace organic contaminants. Analysis of plant and soil samples combined with transport modeling and analysis of transformation products suggested that most of the removal of trace organics and nitrate involved microbial biotransformation under diverse redox conditions. Compared to conventional approaches for removing contaminants from wastewater effluent or reverse osmosis concentrate horizontal levees often are more economical. They also provide additional benefits that may make it easier to obtain the funding needed to build and maintain them.

Multi-contaminant removal in a horizontal levee: A natural approach to reverse osmosis concentrate treatment

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.